Christian Brunet

Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial–interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization—an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below—as invoked in some palaeoclimatic and future climate change scenarios—may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.

Changes in the δ13C of surface water particulate organic matter across the subtropical convergence in the SW Indian Ocean

We have measured the carbon isotopic composition of particulate organic matter suspended in surface waters (POM) between 59°S and 30°S in the SW Indian Ocean during the austral summer. In an attempt to further document the pattern and causes of covariance between POC-δ13C and [CO2aq], we concurrently measured surface water pCO2, temperature, salinity, nitrate concentration, POM concentration, chlorophyll a and the δ13C of total dissolved inorganic carbon. While we found the previously reported general negative correlation between POC-δ13C and [CO2aq], we also observed a prominent maximum in POC-δ13C in the region immediately north of the Subtropical Convergence, coinciding with a maximum in [POM] and chlorophyll a, and with a minimum in pCO2. The increase in POC-δ13C between 59°S and the Subtropical Convergence is consistent with the trend expected if [CO2aq] were the main factor controlling the isotopic composition of POM. In contrast, data from the region north of the Subtropical Convergence clearly illustrate that POC-δ13C can also vary independently of [CO2aq] as a 5 per mil decrease in POC-δ13C was found in a region characterized by nearly constant [CO2aq]. We review several physiological factors which may account for these observations and discuss their implications for paleoceanographic reconstruction of [CO2aq] from the carbon isotopic composition of sedimentary organic matter.

Variability of sources and sinks of CO2 in the western Indian and southern oceans during the year 1991

For the period from January to September 1991 we describe spatial and temporal variations of sea surface carbon dioxide fugacity (fCO2) in the Antarctic, Subantarctic, subtropical, and tropical regions of the Indian Ocean (including the Red Sea). The measurements were made continuously with an infrared technique during seven cruises. We study the temporal variations of fCO2 at daily, monthly and seasonal scales in selected areas. High-frequency variabilities of 20 μatm/d have been observed near polar frontal zone. Both spatial and temporal fCO2 variations are large near the subtropical and Subantartic fronts. In the subtropical domain, fCO2 decreases regularly from austral summer to winter. In January this region is a small CO2 sink with values near equilibrium with the atmosphere. In July, low fCO2 (300 μatm) leads to a CO2 flux of −4.5 mmol/m2/d into the ocean for the zonal band 23°S-35°S. A quantitative study of monthly and seasonal fCO2 budgets is presented for the subtropical area. Considering first the observations at seasonal scale, it is shown that changes in fCO2 can be explained by temperature variations and air-sea exchanges; the sum of biological and mixing processes, considered as the balance of the seasonal fCO2 budget, is close to zero. The monthly fCO2 budgets are then calculated. In that case, other processes must be taken into account to close the budget: the observations indicate that the effect of productivity exceeds the one of mixing in austral summer and the opposite in winter. We then describe the seasonal air-sea fCO2 differences (ΔfCO2) for the whole western Indian Ocean and corresponding Antarctic sector (18,000 observations). In the equatorial and tropical regions the ocean is a CO2 source as was previously observed in the 1960s. In the subtropical area the CO2 sink dominates but varies strongly on a monthly scale. In the circumpolar front zones there is a large potential CO2 sink in summer. In the Antarctic waters, fCO2 spatial variability is very high at mesoscale, especially in the area of the Kerguelen plateau. Finally, it is shown that in some oceanic areas, well-defined relations exist between fCO2 distribution and temperature and salinity. If we want to use them to constrain mappings of continuous fCO2 fields from sparse observations, such relations must be considered at regional and at least seasonal scales.

The densities of western Indian Ocean, Red sea and eastern Mediterranean surface waters

Abstract Direct measurements of density were made on 176 surface samples collected in 1979 from the western Indian Ocean, Red Sea, and eastern Mediterranean Sea. The measurements were compared with the values calculated from the conductance salinity in order to evaluate the influence on the density of the partial molar volumes and the partial molar conductivity of the ions whose ionic ratios differ from their values in Standard Seawater. It is concluded that the differences between the measured and calculated densities are practically constant in vast geographical areas, corresponding to the various water masses of the World Ocean. An exception is the Red Sea, where the differences vary rapidly from the south to the north. These differences are always negative for the surface waters studied and can be correlated linearly to the variation of conductivity salinity. They are only partially explained by the total alkalinity and total carbon dioxide changes in these waters.

Child pedestrian anthropometry: evaluation of potential impact points during a crash

This paper highlights the potential impact points of a child pedestrian during a crash with the front end of a vehicle. Child anthropometry was defined for ages between 3 and 15 years. It was based on the measurement of seven different segment body heights (knee, femur, pelvis, shoulder, neck, chin, vertex) performed on about 2,000 French children. For each dimension, the 5(th), 50(th) and 95(th) percentile values were reported, and the corresponding linear regression lines were given. Then these heights were confronted with three different vehicle shapes, corresponding to a passenger car, a sport utility vehicle and a light truck, to identify impact points. In particular, we show that the thigh is directly hit by the bumper for children above 12 years of age, whereas the head principally impacts the hood. The influence of child anthropometry on the pedestrian trajectory and the comparison with test procedures in regulation are discussed.

Anthropometric characterization of spleen in children

PurposeThis paper aims to characterize the 3D geometry of the child spleen which is still unknown.MethodsAn anthropological measurement protocol, based upon 3D modeling using spleen-computed tomography data, was set up. Characteristic measurements were defined to allow dimensions and spatial localization description from classical anatomical landmarks (11th dorsal vertebra and 10th left rib).ResultsGrowth patterns showed a global enlargement without significant changes in distance to anatomical bone points.ConclusionsThis preliminary study describes a validated measurement protocol based on 3D reconstructions and gives description of the child spleen during growth.

Knee ligaments mechanics From experiments to FE simulations

Acting as track rod for joints, knee ligaments are viscoelastic complex structures which are loaded up to damage and failure during trauma situations. This paper presents 10 years of joint research at the Laboratory of Biomechanics and Application and the Laboratory of Acoustics and Mechanics in investigating the mechanical behaviour of such structures. Staring from clinical knowledge, we show, how experimental, histological, theoretical and FE simulation approaches have been performed to investigate such the behaviour of such structures.

Pedestrian lower limb injury criteria evaluation

In the field of pedestrian injury biomechanics, knees and lower legs are highly recruited during crash situations, leading to joint damage and bones failures. This paper shows how numerical simulation can be used to complete injury mechanism analysis and then to postulate on a knee injury criteria in lateral impact. It focuses on relationships between ultimate lateral bending and shearing at the knee level and potential ligament damage, based on subsystem experimental tests. These ultimate knee lateral bendings and shearings for potential failure of ligaments (posterior cruciate, medial collateral, cruciates and tibial collateral) were estimated at 16° and 15 mm in pure lateral shearing and bending impact tests respectively. Then this methodology was applied on a full test of pedestrian impact.